Valve prostheses, such as e.g. cardiac valve prostheses, can essentially be separated into two basic categories, namely mechanical valve prostheses and biological valve prostheses. Generally, in mechanical valve prostheses, the blood flow through the valve is controlled by one or more obturators including rigid bodies mounted so as to be able to oscillate or “tilt” in a rigid support. In contrast with biological valve prostheses, blood flow is controlled by valve leaflets formed of biological tissue.
The biological valve leaflet material, which is subjected to treatment (stabilization) to render it biologically inert, can be derived from a natural cardiac valve taken from an animal (for example, a natural pig's valve) or can be formed from biological tissue other than valve tissue (for example, bovine pericardium).
Biological valve prostheses may in turn take the form of “stented” valves—where the valve leaflets are mounted on a rigid or slightly flexible stent or armature—and “unstented”, or “stentless”, valves.
Documents EP-A-0 515 324 and U.S. Pat. No. 5,713,953 disclose various embodiments of stentless cardiac valve prostheses, including embodiments where the biological material is replaced (either partially or completely) with an artificial/synthetic material such as a micro-porous and/or composite synthetic material, for example polyurethane.
Stentless valve prostheses exhibit as a whole characteristics of deformability that offer functional advantages due to a great similarity to the anatomy of natural valves.
Implantation of a stentless valve prosthesis, either by conventional thoracic surgery or by minimally-invasive surgical techniques, may involve positioning the prosthesis at the implantation site (e.g. an aortic site) by using a “holder” device.
The holder may, for example, support the prosthesis i) during production of the prosthesis, while the prosthesis is subjected to phases of immersion in treatment liquids, ii) after the valve has been inserted into its package, where it is usually kept immersed in a storage liquid, and/or iii) during implantation to enable the surgeon to implant the prosthesis. Holder devices may include a support or “grip” hub adapted for connection to a manipulation handle. The surgeon can thus locate the prosthesis (fixedly held by the holder) at the implantation site and properly orient it to ensure that the leaflets of the prosthesis are positioned at the same angular locations of the leaflets of the natural valve substituted by the prosthesis. Exemplary of such a holder is the arrangement disclosed in US 2008/0262603 A1, including a grip element from which a plurality of arms extend for supporting a prosthetic heart valve at an intermediate position between the commissures.
In the case of a stentless prosthesis, the deformability of the prosthesis demands a high degree of skill by the intervening surgeon.